Preparation of 2,5-dimethylfuran-3-carboxylic esters

ABSTRACT

Preparation of 2,5-dimethylfuran-3-carboxylic esters by reaction of acyloxypropionaldehyde with an acetoacetic ester.

United States Patent 1 1 Merkle et al.

l l PREPARATION OF LS-DIMETHYLFURAN-3-CARBOXYLIC ESTERS [75] Inventors: Hans Rupert Merkle, Ludwigshal'en;

Hardo Siegel, Speyer. both of Germany [73] Assignee: Badische Anilin- & Soda-Fabrik Aktiengesellschaft, Ludwigshafen (Rhine). Germany [22] Filed: Jan. 3|, 1973 211 Appl. No; 328,480

[58] Field of Search 260/3475 51 Nov. 11, 1975 [56] References Cited OTHER PUBLICATIONS Dunlop and Peters, The Furans," 1953. p. 642, Gurrey. Knoevenagel Reaction, 1954. pp. 103-l04. Gonzalez et al., C.A.," Vol. 49 (5422 f). Williams et al.. "J. Amer. Chem. Soc," Vol. 82. l958. pp. 4883-4888.

Primary Ev\uminerHarry I, Moatz AIIurne), Again, m FirmJohnston, Keil. Thompson. Shurtleff l 7 l ABSTRACT Preparation of 2,5-dimethylfuran-3-curboxylic esters by reaction of acyloxypropionaldehyde with an acetoacetic ester.

6 Claims, N0 Drawings 1 PREPARATION OF 2,S-DIMETHYLFURAN-B-CARBOXYLlC ESTERS The present invention relates to a simple and very efficient process for the production of 2,5-dimethylfuran- 3-carboxylic esters.

It is known from German Patent No. 1,768,686, German Laid-Open Application DOS 2,019,535 and German Laid-Open Application DOS 2,006,471 that furan'3-carboxylic acid derivatives are excellent pesticides, particularly with regard to their fungicidal action. They are produced with 2,5-dirnethylfuran-3- carboxylic acid, which is easily accessible by hydrolysis from 2,5-dimethylfuran-3-carb0xylic esters.

1t is known to produce furan-3-ca-rboxylic acid derivatives by condensation .of B-keto acid derivatives with a-hydroxyketones in the presence of Friedel-Crafts catalysts (Advances Heterocycl. Chem 7, 377, 1966; DOS 2,006,471 It is a disadvantage of this production method that a large amount of catalyst is, required for the reaction, making it difficult toisolate the product upon completion of the reaction. Furthermore, the catalyst attacks the hydroxyl groups in the a-hydroxyketone with the formation of by products.

where ac denotes acyl (formyl, propionyl, butyryl, isobutyryl, preferably acetyl), at a temperature of from 20 to +130C with an acetoacetic ester of the formula U co-oa CH 0 OH; I

where R denotes lower alkyl' (methyl, propyl, isopropyl, butyl, isobutyl, preferably ethyl), are obtained in a simple manner by condensing an a-acyloxypropionaldehyde of the formula The condensation may be carried out without catalysts and at superatmospheric pressure (2 to 700 atmospheres gauge).

Condensation may advantageously be carried out in the presence of a catalyst usually used in the Knoevenagel condensation. Examples of such catalysts are catalytic amounts of a base, e.g., triethylamine, piperidine, pyrrolidine, alanine, pyridine, tri-nbutylamine, cyclohexylamine, sodium hydroxide and potassium hydroxide and their salts, e.g., acetates, hydrochlorides, carbonates and sulfates.

Further Knoevenagel condensation catalysts are described in Advances Heterocycl. Chem., 7, 377, 1966.

Solvents may be used in the condensation, for instance ether, benzene, toluene, chloroform, methylene chloride, tetrahydrofuran and dioxane. The base, e.g.,

pyridine, may also serve as solvent. It is particularly advantageous to carry out the reaction without a solvent.

Condensation may expediently be carried out in the presence of agents which bind water, e.g., dry Na,SO., CaSO ZnO, ZnCl,, CuSO silica gel, A1 0, and M gSO,. However, the water of reaction may also be removed by conventional methods by aze'otropic distillation with the aid of solvents (methylene chloride, benzene, toluene, chloroform).

The second reaction stage is a cyclization. Cyclization of the compound of formula III to the ethyl ester of 2,5-dimethylfuran3-carboxylic acid 1V occurs partially during the Knoevenagel condensation and may be represented as follows:

Cyclization is particularly accelerated by elevated temperature, superatmospheric pressure or by a cyclization catalyst, e.g., an acid, as described in Advances Heterocycl. Chem., 7, 377, 1966 for the cyclization of l,4-dicarbonyl compounds, e.g., toluenesulfonic acid, sulfuric acid, montmorillonite, acidic ion exchangers, ZnCl AlCl and phosphoric acid.

The esters obtained by the process of the invention are pure, and the carboxylic acid obtained from them by hydrolysis may be used direct for the synthesis of active ingredients for use as plant protection agents.

The process of the invention is illustrated by the following examples.

EXAMPLE 1 At to C, 03 part (by weight) of piperidine and 3 parts of Na,SO. were added to a well stirred mixture of 11.6 parts of a-acetoxypropionaldehyde and l3.0 parts of ethyl acetoacetate. The mixture was stirred overnight at room temperature. Gas-chromatographic analysis of the reaction product the following day showed that the condensation product III which had formed had already partially cyclized to the ethyl ester of 2,5-dimethylfuran-3-carboxylic acid IV. The ring was closed by adding 0.2 part of toluenesulfonic acid at 50C.

The ester was dissolved in 0.2 part of 40% ethyl alcohol and hydrolyzed at 70C with [0 parts of 50% caustic solution.

After the mixture had cooled it was acidified with dilute HCl and the yellow precipitate was filtered off and dried.

Yield: 12.4 parts (74%) of 2,5-dimethylfurancarboxylic acid, m.p. I36C.

EXAMPLE 2 carboxylic acid was obtained by distillation; b.p. (0.4

mm Hg): 45 to 51C.

EXAMPLE 3 A mixture of 14.5 parts of a-acetoxypropionaldehyde and l6.25 parts of ethyl acetoacetate was slowly added to 10 parts of pyridine containing a few drops of piperidine; the temperature was maintained at +l0C.

The mixture was then stirred for 8 hours at 40C, and then neutralized with dilute HCI. The oil was worked up as described in Example 2 to the ethyl ester of 2,5- dimethylfuran-3-carboxylic acid.

Yield: 19 parts (90.5%)

At room temperature, 0.5 part of piperidine acetate was added to a solution of l7.4 parts of a-acetoxypropionaldehyde and l9.5 parts of ethyl acetoacetate in 250 parts of benzene. The mixture was then boiled overnight, the water being removed by azeotropic dis- 9 COR F k;

O l-L. CH5 2 where R denotes lower alkyl, wherein an a-acyloxypropionaldehyde of the formula CHO where ac denotes acyl, is condensed in the presence of a catalytic amount of a base at a temperature of from -20 to +l30C with an acetoacetic ester of the formula where R has the above meanings, and the condensation product is cyclized at a temperature of from -20 to +l 30C.

2. A process as claimed in claim 1 wherein condensation is carried out at a pressure of from 2 to 700 atmospheres gauge.

3. A process as claimed in claim I wherein R denotes alkyl having [-4 carbon atoms.

4. A process as claimed in claim 1 wherein the cyclization of the condensation product is carried out in the presence of a catalytic amount of toluene sulfonic acid, sulfuric acid, montmorillonite, an acidic ion exchanger, ZnCl,, AlCl, or phosphoric acid.

5. A process as claimed in claim 1 wherein said a-acyloxypropionaldehyde is a-acetoxypropionaldehyde and said acetoacetic ester is ethylacetoacetate.

6. A process as claimed in claim 1 wherein the cyclization is conducted in the presence of a catalytic amount of an acid.

* I! i I! III 

1. A PROCESS FOR THE PRODUCTION OF AN ALKYL ESTER OF 2, 5DIMETHYLFURANCARBOXYLIC ACID OF THE FORMULA
 2. A process as claimed in claim 1 wherein condensation is carried out at a pressure of from 2 to 700 atmospheres gauge.
 3. A process as claimed in claim 1 wherein R denotes alkyl having 1-4 carbon atoms.
 4. A process as claimed in claim 1 wherein the cyclization of the condensation product is carried out in the presence of a catalytic amount of toluene sulfonic acid, sulfuric acid, montmorillonite, an acidic ion exchanger, ZnCl2, AlCl3 or phosphoric acid.
 5. A process as claimed in claim 1 wherein said Alpha -acyloxypropionaldehyde is Alpha -acetoxypropionaldehyde and said acetoacetic ester is ethylacetoacetate.
 6. A process as claimed in claim 1 wherein the cyclization is conducted in the presence of a catalytic amount of an acid. 